Tom Donilon, the US president's top security aide, arrived in Tel Aviv on Saturday morning for three days of meetings with Israeli defence and security chiefs.

While Washington claims the visit is simply the latest in a series of "regular, high level consultations between the United States and Israel", it came just days after coordinated attacks launched against Israeli embassies across the world provoked outrage in Jerusalem, which claims with certainly that Iran is responsible.

Israel'soption of launching a strike on Iranian nuclear facilities was expected to be the urgent topic of discussion during Mr Donilon's visit.

Hours before he arrived Iran's navy claimed its warships entered the Mediterranean to show its 'might' to regional countries.

In recent weeks, Israeli government officials have remained resolutely tight-lipped on their position on the Iranian threat but a string of high-ranking US officials have expressed the belief that Israel is preparing to act, with or without American support.

The rising tensions came as Foreign Secretary William Hague warned in Saturday's edition of The Daily Telegraph of the danger of a nuclear Cold War in the Middle East because of Iran's nuclear programme.

Mr Donilon's visit follows a trip by Mossad chief Tamir Pardo to Washington in December to discuss the possibility of military action against Iran, in which the security chief asked his counterparts in the CIA what the US reaction would be to an independent Israeli attack on Tehran.

In an interview with the New York Times late last year, Ehud Barak, Israel's minister of defence, suggested that an Israeli strike on Iran is all but inevitable.

General Uzi Eilam, a former director general of Israel's ministry of defence, revealed earlier this week that he may be "among the only ones [Israeli defence officials]" who does not think a strike is necessary.

He added that the perception of Iran's nuclear threat has, in his opinion, been overblown. "I don't accept that there has been an urgent deterioration [in attempts to prevent a nuclear Iran]," he said.

"I would be more reserved as far as ringing the big bell goes. But if a country like Iran is determined to develop a nuclear weapon, sooner or later they will get there. If a poor country like North Korea can do it, so can Iran. The question is: how soon can they get there?"

Iran remains adamant that its nuclear development is for peaceful purposes. It announced three significant advances this week, including the development of centrifuges capable of producing higher quality enriched uranium in a bigger quantities and more quickly that its old technology.

A letter written by Tehran expressing a willingness to discuss its nuclear activity was received with cautious optimism on Friday.

Victoria Nuland, the US State Department spokeswoman, said Washington and its allies were wary of "false starts" to a negotiation process.

"We've had negotiations that started and fizzled, or negotiations that ate up a lot of time and didn't go where they needed to go," Nuland said.

Israel is yet to react to the letter. Following the botched attempts to bomb Israeli embassy staff in Israel, Georgia and Thailand, Prime Minister Benjamin Netanyahu urged the international community to "draw a red line" under Tehran's efforts to promote terrorist activity.

"Iran is the biggest exporter of terror in the world. Iran's terror operations are now exposed for all to see," Mr Netanyahu told Knesset members.

Leon Panetta, the US defence secretary, has indicated in his clearest terms yet that Washington will act to prevent a nuclear Iran and will not tolerate it if Iran attempts to block the Straits of Hormuz, a naval trade route supplying one fifth of the world's oil.

"We, the United States, have all options on the table," he said.

"If you're a nation that wants to be part of the international family of nations, then join it... Join us in an effort to try to diplomatically reduce your efforts in terms of nuclear capability," Panetta said.

"So that pressure needs to continue, and Israel has been part of that. My hope is that Israel will be part of that international effort to keep the pressure on. That's the most effective way to isolate Iran and to keep the pressure on," he added.

Alain Juppe, the French foreign minister, said on Thursday that a two-day visit to Iran by top UN nuclear watchdog officials scheduled would help determine whether Tehran was serious about tackling international concerns.